Add hints for dealing with bad PPMs on Windows

Resolves #636

Author: hollasch

books/RayTracingInOneWeekend.html

@@ -171,11 +171,19 @@
     [Listing [first-img]: First image output]
 </div>
 
-If it doesn’t, then you probably just have some newlines or something similar that is confusing the
-image reader.
-
-If you want to produce more image types than PPM, I am a fan of `stb_image.h`, a header-only image
-library available on GitHub at https://github.com/nothings/stb.
+If it doesn’t, then you may just have some line-ending differences or something similar that is
+  confusing the image reader.
+To help debug this, you can find a file `test.ppm` in the `images` directory of this project to
+  ensure that your viewer can handle this format, and to use as comparison for a valid PPM file.
+
+Some readers have reported problems viewing their generated files on Windows.
+In this case, the problem is often that the PPM is written out as UTF-16, often from PowerShell.
+If you run into this problem, see
+  [Discussion 1114](https://github.com/RayTracing/raytracing.github.io/discussions/1114)
+  for help with this issue.
+
+If you want to produce other image formats, I am a fan of `stb_image.h`, a header-only image library
+  available on GitHub at https://github.com/nothings/stb.
 
 
 Adding a Progress Indicator